Tumour cells wholly or partly elude regulation and control by the body and are characterised by uncontrolled growth. This is due on the one hand to the loss of control proteins such as for example Rb, p16, p21 and p53 and also to the activation of so-called accelerators of the cell cycle, the cyclin-dependent kinases.
Studies in model organisms such as Schizosaccharomyces pombe, Drosophila melanogaster or Xenopus laevis as well as investigations in human cells have shown that the transition from the G2 phase to mitosis is regulated by the CDK1/cyclin B kinase (Nurse 1990, Nature 344: 503-508). This kinase, which is also known as “mitosis promoting factor” (MPF), phosphorylates and thereby regulates a plurality of proteins, such as e.g. nuclear lamina, kinesin-like motor proteins, condensins and Golgi Matrix Proteins, which play an important part in the breakdown of the nuclear coat, in centrosome separation, the structure of the mitotic spindle apparatus, chromosome condensation and breakdown of the Golgi apparatus (Nigg. E. 2001, Nat Rev Mol Cell Biol. 2(1):21-32). A murine cell line with a temperature-sensitive CDK-1 kinase mutant shows a rapid breakdown in CDK-1 kinase after temperature increase and a subsequent arrest in the G2/M phase (Th'ng et al., 1990, Cell. 63(2):313-24). The treatment of human tumour cells with inhibitors against CDK1/cyclin B, such as e.g. butyrolactone, leads to an arrest in the G2/M phase and subsequent apoptosis (Nishio, et al. 1996, Anticancer Res. 16(6B):3387-95).
Moreover, the protein kinase Aurora B has also been described as having an essential function during entry into mitosis. Aurora B phosphorylates histone H3 on Ser10 and thereby initiates chromosome condensation (Hsu et al. 2000, Cell 102:279-91). A specific cell cycle arrest in the G2/M phase may, however, also be initiated e.g. by inhibition of specific phosphatases such as e.g. Cdc25C (Russell and Nurse 1986, Cell 45:145-53). Yeasts with a defective Cdc25 gene arrest in the G2 phase, whereas overexpression of Cdc25 leads to premature entry into the mitosis phase (Russell and Nurse, 1987, Cell 49:559-67). Moreover, an arrest in the G2/M phase may also be initiated by inhibition of specific motor proteins, the so-called kinesins such as for example Eg5 (Mayer et al., 1999, Science 286:971-4)), or by microtubuli stabilising or destabilising agents (e.g. colchicin, taxol, etoposide, vinblastine, vincristine) (Schiff and Horwitz 1980, Proc Natl Acad Sci USA 77:1561-5).
In addition to the cyclin-dependent and Aurora kinases the so-called polo-like kinases (PLK), a small family of serine/threonine kinases, also play an important role in the regulation of the eukaryotic cell cycle. Hitherto, the polo-like kinases PLK-1, PLK-2, PLK-3 and PLK-4 have been described in the literature. PLK-1 in particular has been found to play a central role in the regulation of the mitosis phase. PLK-1 is responsible for the maturation of the centrosomes, for the activation of phosphatase Cdc25C, as well as for the activation of the Anaphase Promoting Complex (Glover et al. 1998, Genes Dev. 12:3777-87; Qian et al. 2001, Mol Biol Cell. 12:1791-9). The injection of PLK-1 antibodies leads to a G2 arrest in untransformed cells, whereas tumour cells arrest during the mitosis phase (Lane and Nigg 1996, J Cell Biol. 135:1701-13). Overexpression of PLK-1 has been demonstrated in various types of tumour, such as non-small-cell carcinoma of the lung, plate epithelial carcinoma, breast and colorectal carcinoma (Wolf et al. 1997, Oncogene 14:543-549; Knecht et al. 1999, Cancer Res. 59:2794-2797; Wolf et al. 2000, Pathol. Res. Pract. 196:753-759; Takahashi et al. 2003, Cancer Sci. 94:148-52). Therefore, this category of proteins also presents an interesting point of attack for therapeutic intervention in proliferative diseases (Liu and Erikson 2003, Proc Natl Acad Sci USA 100:5789-5794).
The resistance of many types of tumours requires the development of new drugs for combating tumours. The aim of the present invention is therefore to indicate new active substances which may be used for the prevention and/or treatment of diseases characterised by excessive or anomalous cell proliferation.